Rapid, accurate detection methods for pathogenic bacteria are important to the food and dairy industries. Pathogens such as Escherichia coli O157:H7 and Salmonella spp. are the leading cause of food borne disease outbreaks and cases of known etiology, and have been implicated in outbreaks from consumption of contaminated ground beef, dairy products, and fruit juices. Recent outbreaks illustrate the continued threat bacterial pathogens present to the food supply and consumers. The possibility of contamination postprocessing and at the point of retail sale makes rapid methods vital to consumer safety.
Antibody-based methods such as enzyme-linked immunosorbent assays (ELISA) are commonly used to rapidly detect food borne pathogens such as E. coli O157:H7 and Salmonella spp., but assay functionality is influenced by environmental factors in the food matrix including pH, salt concentration, and water activity. Enrichment is necessary to overcome matrix effects and to achieve cell concentrations within assay detection limits. Detection by ELISA is specific, but both live and dead cells can elicit an antigenic response. Identification of viable cells is important for the food industry, due to the low infectious doses of E. coli O157:H7 and Salmonella. Differentiation between live and dead cells can be achieved through bioluminescence assays, which have been used to detect and quantify bacteria in food products including milk, ground beef, produce, and juices. These assays are nonspecific, but have demonstrated more sensitivity than have traditional methods.
A combination of techniques is required to achieve desired sensitivity and specificity and to identify viable cells. Most methods for the detection of viable E. coli O157:H7 and Salmonella spp. in food products combine immunomagnetic separation (IMS) with culture methods, flow cytometry, or PCR. IMS is designed to concentrate a sample for use in detection assays that have high levels of detection (LOD), but capture efficiency is affected by cell concentration, particulate interference, and nonspecific binding. IMS has also been coupled to fluorescence and chemiluminescence for rapid, specific detection of viable cells in various food matrices. A limited number of IMS-bioluminescence assays have been reported, and have primarily been used to demonstrate the efficiency of biosorbents. The efficacy of these assays in complex samples has not been shown.
Bioluminescence assays would have greater utility if viable pathogens could be reliably identified directly from complex matrices. Therefore, what is need is a rapid ATP bioluminescence immunoassay (ATP-BLIA) for detection of viable cells directly from food samples, while maintaining sensitivity and specificity.